1. Field of the Invention
The present invention relates to a method of dry etching an oxide film containing In, Ga, and Zn (hereinafter, referred to as “In—Ga—Zn—O”). In particular, the present invention relates to a method of dry etching an oxide semiconductor film containing In—Ga—Zn—O which is employed in producing a fine electronic component such as a semiconductor device, a semiconductor integration circuit, and an electrode.
2. Description of the Related Art
In recent years, as disclosed in Japanese Patent Application Laid-Open No. 2004-103957, research and development of a semiconductor oxide film containing In—Ga—Zn—O and its deposition conditions has been extensively conducted. Particularly because the semiconductor oxide film can be formed on a resin film at low temperature, its future application of the semiconductor oxide film to a portable electronic product with light weight has been targeted.
Hitherto, the patterning of a produced film containing In—Ga—Zn—O or Ga—Zn—O has been performed by a lift-off process. The lift-off process is disclosed in, for example, K. Nomura et al., Nature, Vol. 432, 25 Nov. 2004, pp. 488-492, or E. M. C. Fortunato et al., Advanced Materials, 2005, 17, No. 5, pp. 590-594.
Japanese Patent Application Laid-Open No. H11-335874 discloses the use of a process gas containing methane for a dry etching process for a conventional transparent conductive oxide film, for example, a zinc oxide (ZnO) film.
Japanese Patent Application Laid-Open No. H03-077209 discloses a technique in which when a transparent conductive film containing ITO formed on a glass substrate is subjected to a dry etching process, reactive dry etching using a mixed gas of hydrogen and carbon hydride is performed while heating the ITO film. In addition, Japanese Patent Application Laid-Open No. H10-087301 discloses a technique of dry etching a conductive film containing SnO2, In2O3, and ZnO as main components by using hydrogen iodide.
In the conventional dry etching method for a semiconductor film, a fluorine-based gas is used as an etching medium in many cases.
However, the lift-off process as described above has a problem that a photoresist is melted and deformed at high temperature. The lift-off process has another problem that when a photoresist is removed, an edge of a pattern of a deposited film is curved up, and thereafter an electric wire crossing over the pattern edge is liable to be broken, which lowers the production yield.
In addition, a photoresist patterned by photolithography is used as an etching mask for reactive ion etching (RIE). In this case, there arises a problem that a non-volatile substance is deposited on a surface of the photoresist after the etching, which makes it difficult to remove the photoresist even cleaned by an ultrasonic wave.
Accordingly, to process a film containing In—Ga—Zn—O, various etching methods for obtaining a pattern having high reproducibility and a desired shape have been studied. The etching method is roughly classified into two methods. One is wet etching in which a sample is immersed in a chemical agent, and the other one is dry etching utilizing a gaseous etching medium. In principle, the etching proceeds isotropically in the wet etching, so that there arises a problem of generating a phenomenon such as an undercut beneath a mask, peeling of a pattern due to adhesion insufficiency between the mask and the processed film, and permeation of an etchant. There arises another problem that an etching residue floats or remains on the surface of a device. Consequently, it is necessary to replace the etching liquid frequently, and that leads to large consumption of the etching liquid.
On the other hand, the dry etching method has an advantage that chemically active ions generated in a plasma bombard vertically on the surface of the substrate, so that the etched shape is faithfully transferred from the mask pattern.
As a general dry etching method, a RIE method is used. The principle of RIE is simply described as follows. An etching gas is introduced into a vacuum chamber with parallel plate electrodes, and a high frequency power is applied to the electrodes. Electrons accelerated to a high speed in a high frequency electric field ionize an etching gas due to electrolytic dissociation to form a plasma state. Radicals and ions generated in the plasma cause an etching reaction on a substrate surface. The main etching mechanisms are as follows. One thereof is a chemical reaction where active species are adsorbed onto the substrate surface to form a secondary product and then released. Another one is a physical reaction, such like a sputtering effect, where accelerated positive ions collide with the substrate to physically bombard the substrate.
However, the above-mentioned documents do not explicitly disclose the dry etching to an In—Ga—Zn—O film.
Further, the dry etching method described in Japanese Patent Application Laid-Open No. H03-077209 addressed a problem that, in a case where ITO is not heated, An In and carbon compound byproduct are deposited on the ITO film, which makes it difficult to obtain a pattern of a desired shape. Moreover, applicability of the method to a film containing In—Ga—Zn—O, an etch rate thereof, and the like are not described therein.